Simonetta is a family name as is Cavazzi della Somaglia. This made finding anything about the Countess impossible. Spanish ancestry is all but certain because she is depicted, probably about the time of her marriage, wearing a tontillo.

From Wikimedia; shadows filled in and exposure increased. The dark areas are very, very dark.

The Countess wears a black tontillo with a spectacular lace bertha, depicted in breathtaking detail, in this Cittadini portrait.